The development of a technique about a system capable of reliably extracting a three-dimensional (3D) shape of a surface of a moving metal object in real time has been required. In particular, in the steel industry, great efforts have been made to improve the quality of final release products by finding a variety of surface defects associated with the final release products and by excluding a product from which a surface defect is found, and the development of a related technique has been consistently required.
A photometric stereo method refers to a method of extracting a 3D shape of an object using images acquired by sequentially irradiating minimum at least three lights to a target object using a single camera. According to an increase in a number of lights, the 3D shape of the target object may be more reliably extracted. Such an existing method of acquiring images by sequentially irradiating minimum at least three lights in different directions may not provide an image captured at the same viewpoint with respect to a moving object. Accordingly, the extraction of a 3D image may be difficult.
Currently, to solve the above issue, a method of extracting 3D shape information by simultaneously irradiating, to an object, lights of different three wavelengths, red (R), green (G), and blue (B) wavelengths, using a single RGB camera has been developed. In general, a metal surface refers to a non-Lambertian surface on which a direct reflected light is present in a predetermined direction when irradiating a light. When simultaneously irradiating three lights of three R, G, and B wavelengths to a metal object, a direct reflected light may be transferred to a camera based on a position of a corresponding light and a shape of a surface of the metal object to thereby saturate a sensor of the camera. It indicates that the extraction of a 3D shape of a target object is difficult or inaccurate.
Accordingly, there is a need for a method and system that may overcome the above issues and may reliably extract a 3D shape of a surface of a metal object.